This invention relates to a hybrid-type magnet and a stepping motor including the same, and more particularly to a hybrid-type magnet wherein a permanent magnet and an electromagnet are combined with each other to control a current fed to the electromagnet, to thereby control intensity of a magnetic field affecting an exterior of the hybrid-type magnet and generate energy increased in amount as compared with energy fed thereto.
There have been conventionally developed few magnets constituted by a combination of a permanent magnet and an electromagnet. It is generally considered that a combination of a permanent magnet and an electromagnet exhibits a function of generating a sum of a magnetic field of the permanent magnet and that of the electromagnet when a current is flowed through an excitation coil of the electromagnet in a certain direction. Also, it is considered that the combination, when a current in a direction opposite to the above-described direction is flowed through the excitation coil, causes a magnetic field of the permanent magnet to be canceled by a magnetic field in an opposite direction generated by the electromagnet.
Thus, when the excitation coil does not have a current flowed therethrough, only the permanent magnet generates a magnetic field. Flowing of a current through the excitation coil leads to an increase or decrease in magnetic.
However, such a combination of the permanent magnet and electromagnet as described above fails to effectively utilize energy of the permanent magnet. Energy of the permanent magnet is apparently utilized, however, it is required to feed energy to the electromagnet for canceling the magnetic field, resulting in the balance between energy utilized and that fed being zero. Thus, in order to ensure that energy of the permanent magnet is effectively utilized by excitation of the electromagnet, it is required to view the combination from a different angle.
The present invention has been made in view of the foregoing problem of the prior art.
Accordingly, it is an object of the present invention to provide a hybrid-type magnet which is capable of effectively utilizing energy of a permanent magnet by excitation of an electromagnet.
It is another object of the present invention to provide a stepping motor having such hybrid-type magnets as described above incorporated therein.
In accordance with one aspect of the present invention, a hybrid-type magnet is provided. The hybrid-type magnet generally includes an electromagnet and a bar-like engagement member. The electromagnet includes a core made of a magnetic material and formed of a core body and a pair of opposite arms to have a U-shape and an excitation coil wound on the core. The bar-like engagement member includes a permanent magnet and magnetic members arranged so as to interpose the permanent magnet therebetween and is closely joined to outer ends of the arms while being extended between the outer ends of the arms. The permanent magnet is positioned between the arms of the core.
In a preferred embodiment of the present invention, the permanent magnet and magnetic members of the engagement member each have a cross section formed to have a rectangular shape and identical dimensions.
In a preferred embodiment of the present invention, each of the arms of the core has an outer surface defined at a lateral end thereof and the engagement member has end surfaces defined at opposite lateral ends thereof. The outer surface of the arm and one of the end surfaces of the engagement member are formed so as to be flush with each other when the engagement member is closely joined to the core.
In a preferred embodiment of the present invention, the magnetic members of the engagement member each have a saturation magnetic flux density greater than that of the core.
In a preferred embodiment of the present invention, the arms of the core are each formed to have a rectangular shape in cross section.
In a preferred embodiment of the present invention, the engagement member is so constructed that a ratio between a width of the permanent magnet in a direction of magnetization thereof and a sum of widths of the magnetic members is within a range between 1:1 and 1:15.
In a preferred embodiment of the present invention, the core is made of pure iron and the permanent magnet is made of neodymium.
Such construction of the hybrid-type magnet, when the excitation coil of the electromagnet is kept from being fed with a current, permits a line of magnetic force generated by the permanent magnet to form a closed magnetic path passing through the N pole of the permanent magnet, one of the magnetic members, the core, the other of the magnetic members and the S pole of the permanent magnet, to thereby substantially prevent leakage of a magnetic flux to the air. Then, when a current is fed to the excitation coil of the electromagnet to permit the excitation coil to generate a magnetic flux in a direction opposite to the line of magnetic force of the permanent magnet, a line of magnetic force of the permanent magnet is canceled by that of the electromagnet. Also, it is discharged to the air when it exceeds a saturation state of the permanent magnet. At this time, when the amount of magnetic flux of the electromagnet is substantially increased, the amount of magnetic flux discharged to the air corresponds to addition between a magnetic flux of the permanent magnet and that of the electromagnet.
Thus, arrangement of a magnetic element in proximity to the engagement member keeps the hybrid-type magnet from attracting the magnetic element when a current is not flowed through the excitation coil and permits the permanent magnet and electromagnet to cooperate with each other to attract the magnetic element when a current is flowed through the excitation coil. This results in the hybrid-type magnet of the present invention effectively utilizing an action of the permanent magnet free of energy consumption.
Also, in accordance with this aspect, a hybrid-type magnet is provided. The hybrid-type magnet generally includes an electromagnet and a bar-like engagement member. The electromagnet includes a core made of a magnetic material and formed of a pair of core bodies and three arms to have a substantially E-shape and excitation coils wound on the core. The excitation coils are each wound on a corresponding one of the core bodies. The bar-like engagement member includes a first magnetic member, a first permanent magnet, a second magnetic member, a second permanent magnet and a third magnetic member tightly connected to each other in order and is closely joined to the core while being extended between outer ends of outer two arms of the arms of the core. The first and second permanent magnets are each positioned between an adjacent two of the arms.
In a preferred embodiment of the present invention, the permanent magnets and magnetic members of the engagement member each have a cross section formed to have a rectangular shape and identical dimensions.
In a preferred embodiment of the present invention, each of the outer two arms of the arms of the core has an outer surface defined at a lateral end thereof and the engagement member has end surfaces defined at opposite lateral ends thereof. The outer surface of each of the outer two arms of the arms and one of the end surfaces of the engagement member are formed so as to be flush with each other when the engagement member is closely joined to the core.
In a preferred embodiment of the present invention, the magnetic members of the engagement member each have a saturation magnetic flux density greater than that of the core.
In a preferred embodiment of the present invention, the arms of the core are each formed to have a rectangular shape in cross section.
In a preferred embodiment of the present invention, the permanent magnets are formed to have identical widths in a direction of magnetization thereof. The engagement member is so constructed that a ratio between a sum of widths of the permanent magnets and a sum of widths of the magnetic members is within a range between 1:1 to 1:15.
In a preferred embodiment of the present invention, the core is made of pure iron and the permanent magnets are each made of neodymium.
In accordance with another aspect of the present invention, a stepping motor is provided. The stepping motor generally includes a stator and a rotor. The stator includes a plurality of the above-described hybrid-type magnets. The hybrid-type magnets are integrally combined together and arranged in such a manner that the arms are radially extended and spaced from each other at equal angular intervals around a single common core body of the cores of the hybrid-type magnets. The rotor includes magnetic members arranged at equal angular intervals outside the engagement members of the hybrid-type magnets.
In a preferred embodiment of the present invention, a plurality of the stepping motors are arranged at a predetermined phase difference while being connected in series to each other.
Such construction of the stepping motor permits energy increased in amount compared with that fed to the electromagnet to be outputted therefrom by means of the permanent magnet by flowing a pulse current through each of the excitation coils.